The prevalence of HIV is alarmingly high among adults with severe mental illness (SMI), and a large proportion engages in sexual and substance use behaviors that place them at risk for infection. Unfortunately, the link between psychopathology and HIV risk is poorly understood. While psychiatric symptoms likely have a direct influence on risk behavior, the indirect effects associated with SMI may also play an important role. Unstable relationships and interpersonal violence have frequently been implicated as risk factors for HIV, but this association has not been empirically examined among adults with SMI. The proposed study will address this gap in the literature by exploring the social contextual determinants of HIV risk behavior in this population. The specific aims are to: (1) examine the effect of psychiatric illness (diagnosis and symptoms) on HIV risk behavior, (2) consider the influence of sexual/physical abuse and (3) examine the role of social networks and relationship quality. Participants will include 100 adults with SMI primarily schizophrenia, schizoaffective disorder, bipolar disorder, and major depression, who live in transitional housing programs in New York, NY and New Haven, CT. Data will be collected through face-to-face interviews using standardized clinical instruments and will be analyzed using structural equation modeling. The information derived from this study will be useful in developing risk-reduction interventions that are sensitive to the specific needs of adults with SMI, including their interpersonal context.